The modulation of nociception by novel factors including the steroid hormone ecdysone in the fruit fly will be investigated. The fruit fly Drosophila melanogaster model system has produced a quantity of data relevant to higher functions of the human nervous system, including findings in memory processing, sleep, drug abuse and addiction. Exploration of the neurogenetic and hormonal mechanisms controlling nociception in flies will increase our understanding of pain in humans. Using a mutant allele of the ecdysoneless (ecd^) steroid availability gene, we have shown in preliminary studies that when ecdysone is depleted in adult flies, they become hypersensitive to noxious thermal and chemical stimulation. This suggests that steroid signaling has an antinociceptive role in the fly, as has been shown in mammals. This finding establishes the fruit fly as a valid model for the study of steroid modulation of nociception, with implications extending to higher organisms such as humans. We will now characterize the cellular and subcellular nature of ecdysone's role in nociception, and identify other novel genes that are connected to antinociception in the fly. Aim 1 will test for alterations in nociception in flies with manipulated ecdysone levels. A temperature sensitive mutant allele of ecdysoneless, along with other mutants, will be used to ask whether ecdysone levels affect perception of, and behavioral responses to, noxious thermal, chemical and mechanical stimuli. Aim 2 will examine the mode of nociceptive ecdysone signaling in ecdysone receptor mutants. Experiments are designed to test whether disruption of ecdysone signaling at the level of the nucleus or at the membrane affects nociception, thereby determining if the mechanism of nociceptive modulation is a genomic or membrane process. Aim 3 will test for steroid modulation of identified nociceptive neurons. The potential role of ecdysone in the activity of known TRP channel-expressing nociceptive neurons will be assessed by temporal- and cell-specific blockade of signaling using genetic techniques. A parallel electrophysiological approach will also be used to analyze the response of TRP channel-expressing nociceptive neurons to varying levels of the steroid ecdysone. Aim 4 will screen a genome-wide mutant library to identify novel genes connected to antinociception in the fly. We will use a simple food-choice assay to rapidly identify mutants that are hypersensitive to a noxious chemical stimulus (mustard oil). This work should point to potentially novel human therapeutic drug targets.